Extracellular ATP is a messenger in the transduction of noxious stimuli by pain-sensing neurons (nociceptors). The cloning of the sensory neuron-specific ATP-gated ion channel P2X3 generated intense investigation into the ability of ATP to directly activate nociceptors. However, we have new evidence that sensory neurons also express members of a family of G protein-coupled receptors (P2Y receptors) that respond to ATP or related compounds and contribute to nociceptive signaling. These receptors are poorly characterized in neurons: of the 8 known family members only P2Y1 and P2Y2 have been evaluated in sensory neurons and both have been implicated in nociceptive signal transduction. P2Y receptors can be divided into 2 groups based on their coupling to signal transduction pathways;we hypothesize that Gq-coupled receptors are proalgesic while Gi- coupled receptors are analgesic. This proposal consists of 3 Specific Aims designed to identify which P2Y family members contribute to nociceptive signaling and may be useful targets for therapeutic intervention in pain. Specific Aim 1 will use quantitative PCR, immunohistochemistry and Wester blotting techniques to determine which P2Y receptors are expressed in sensory neurons and whether expression changes in response to inflammatory injury. Specific Aim 2 will characterize excitatory and inhibitory actions of Gq-coupled and Gi-coupled P2Y receptors in dissociated sensory neurons using calcium imaging and post-hoc immunocytochemistry. Specific Aim 3 will examine the contribution of P2Y ADP receptors to behavioral pain response thresholds in vivo and will determine whether pharmacological or genetic manipulation of P2Y receptors is analgesic in models of acute and persistent inflammatory pain. These studies will demonstrate the contributions of a new family of receptors to sensory neuron signaling and will provide valuable insight into the mechanisms through which nucleotides act as signaling molecules in the setting of persistent pain.Experiments in this proposal will test the hypothesis that members of the P2Y family of nucleotide receptors are powerful regulators of nociceptor sensitivity that play an important role in the maintenance of persistent pain. We will directly test the possibility that manipulation of these receptors, including the use of antagonists already in development for clinical treatment of non-pain-related syndromes, is an effective analgesic treatment in animal models of persistent pain.